A COMPARISON OF SILYLIDENE-AMINES, SILYLIDENE-PHOSPHANES AND SILYLIDENE-ARSANES - SYNTHESES AND QUANTUM-CHEMICAL CALCULATIONS

A review of recent results of the syntheses, spectroscopic properties - including some cyclovoltametric measurements - and aspects of the mo lecular structures of silylideneamines (silanimines, R(2)Si=NR), silyl idenephosphanes (phosphasilenes, R(2)Si=PR) and silylidenearsanes (ars asilenes, R(2)Si=AsR) is presented. Owing to the distinctly different Si=X bond polarities (X = N, P, As), the molecular structure and the r eactivity of silanimines are quite different from those of the phospho rus and arsenic analogs. The electronic structure of phosphasilenes is distinguishable from that of arsasilenes by means of cyclovoltametric measurements. Whereas the Si=P system undergoes a reversible one-elec tron reduction, the arsenic analogs show exclusively an irreversible r eduction process. The tremendous differences between the Si=N, Si=P an d Si=As bonds are also explored by theoretical investigations of the p arent systems H2Si=NH, H2Si=N-SiH3, H2Si=PH, H2Si=P-SiH3 and H2Si=AsH.